Toxic Algae: A Threat to Florida Waters?
When I was a little girl, my friends and I enjoyed wading in the waters of the Central Florida lake I live on. We would catch tadpoles and swim carelessly in the water, never thinking about what might actually be in it. The only thing we were aware of was that we couldn't see our feet after a few steps because the water was so green. A few years later, on August 26, 2001, I read a shocking headline in my local paper, the Orlando Sentinel . It read "Health Menace Lurks in Lakes." This article led me to wonder whether "killer algae" exist in my lake. If they do, why are they there, and what could we do to get rid of them? This newspaper report about blue-green algae made me suspect that we probably did have toxic algae living in my lake, Spring Lake. I wanted to investigate this question further-certainly before my father tried to teach me how to wakeboard!
I found out that there are a few blue-green algae species that are known to cause health problems and even death. Three species found in freshwater lakes in Florida are Anabaena flos-aquae , Microcystis aeruginosa , andCylindrospermopsin (Florida Lakewatch, 1999). Cylindrospermopsin is an invasive species that is thought to have appeared in Florida about 30 years ago. Since then, it has invaded many Central Florida lakes and has reached toxic levels in some lakes. The blue-green algae in Florida lakes were recently studied by the Florida Department of Health (St. Amand, 2002). Furthermore, the World Health Organization has recognized and studied the algae's harmful effects and set consumption toxicity levels in 1998 (Chapman, 2001). Algae thrive in warm, shallow waters with high nutrient levels. Algae blooms can last for months, and Cylindrospermopsis is a unique species of algae that continually produces toxins.
After this research, my next step was to determine the trophic state of my lake. The Trophic State Classification System is used universally by researchers to group water bodies according to their "degree of biological productivity" (Florida Lakewatch, 1999). The four trophic states, from the lowest level of productivity to the highest, are oligotrophic, mesotrophic, eutrophic, and hypereutrophic. Oligo means "scant or lacking," meso means "mid-range," eu means "good or sufficient," and hyper means "overabundant" (Florida Lakewatch, 1999). If Spring Lake were eutrophic, which is Greek for "well fed," it would be a perfect, nutrient-rich environment for toxic algae.
I called the City of Orlando, and they gave me the phone number of Maurice Gioseffi of the Orlando Lakewatch program. I was hoping that he could just tell me whether we had "killer algae" in my lake, but he convinced me that if I were really interested in the health of my lake, I should participate in Lakewatch. He came over to my house the next weekend to train me to collect lake data and water samples. He said that Lakewatch asks residents to help with its program of monitoring the health of Central Florida lakes.
Rachel collecting and testing her water samples
I was trained in how to collect samples from our lake. He taught me how to do water-clarity readings using a Secchi disc, depth readings, proper sample collections, and how to filter the samples using a vacuum pump. I put the filtered samples in a desiccant jar and took the water and chlorophyll samples to the freezer at the city's lab, where they would then be sent to the University of Florida in Gainesville. There, researchers would measure three things: the amounts of nitrogen, phosphorus, and chlorophyll present. These three things would give us indicators of how healthy the lake was. I learned from the materials he gave me that most of the algae in Florida lakes is blue-green algae—the very kind that includes toxic species. It is important to find out if you have a lake with too much algae, because algae blooms create conditions in which toxins are released. At all of my sampling sites I observed that the Secchi disc disappeared at only 9/10 of a foot (the readings on the rope were in tenths of a foot). That is a very opaque, nutrient-rich lake! I also found that my lake has a mean depth of about 10.8 feet.
My data is recorded in the Lake Water Quality Report , produced annually by the Stormwater Utility Bureau of the City of Orlando. I finally got to see the results of my initial sample collections (I have now been collecting and sending samples for the yearly report for three years). The report said that Spring Lake is a eutrophic lake, hitting hypereutrophic levels in the summer months! The researchers at Gaineville measured the amount of chlorophyll- a in the samples I sent them, as well as phosphorus and nitrogen levels. Chlorophyll is the green pigment found in plants. Almost all algae are green, so the concentration of chlorophyll- a is measured to indicate the amount of algae present in the water body. Chlorophyll- a values greater than 20 mg/m3 are used by the city to identify problem lakes, and Spring Lake had a mean value of 41 mg/m3 ( Lake Water Quality Report , 2000).
That was one answer to my question, but now I had to look further to find out why Silver Lake is eutrophic. As I kayak around my lake, I see that it is triangular in shape. On one side of the triangle is a golf course, and on the other two sides are either houses or the Orange Blossom Trail, a highway. Most of the homeowners on my lake clear out all the emergent plants so that they can see the lake better from their house, or so they can make a beach. Some people say that they clear out their waterfront because they don't want water moccasins to nest by their house. But I noticed that one house actually had beautiful emergent flowering plants and flowering lily pads in front of it. I paddled closer and took some pictures.
When I got home, I researched the plants and found that the beautiful yellow flowers were golden canna and the purple small flowers were pickerelweed. They had white swamp lilies that looked like huge stars as well as banana lilies floating out toward the middle of the lake (Aquatic, Wetland and Invasive Plant Particulars and Photographs, 2005). All of the plants were native Florida plants. With that in mind, I started wondering why only weed-like grasses grew up along the shoreline around the rest of the lake. I walked over and talked to the neighbors with the water garden, and they said that they had planted these natives because they had been told that these plants acted as a filter for the runoff from yard fertilizers. I realized that if these native plants were the only filters our lake had, it was probably full of pollutants from all the other areas where runoff ran straight into the lake. One problem with fertilizer runoff from yards and golf courses is that it can decrease the amount of oxygen in the water, thus stimulating algae growth and perhaps causing a fish kill.On my way home, right in front of that same neighbor's house, I saw a drain from the street. I looked down into it, but I didn't see a screen or basket to catch trash before it went into the lake. I walked back down to the lake and saw a huge pipe draining into the lake. The next day I paddled around our lake looking for pipes. There was one leading from Orange Blossom Trail (OBT) down to the lake, and another between two yards leading into the lake. I looked out my window as we drove along OBT later in the week and saw that it is lined with trash. I wondered to what degree pollutants from surrounding streets drained into the lake. This led me to try to find out the size and shape of the watershed. I have drawn a picture of the watershed and the storm drains that empty pollutants and nutrients into Spring Lake.
My observations told me why our lake was eutrophic, but I still had not determined whether we had any toxic algae species in our lake. I found pictures of toxic algae to compare to what I saw under the microscope. I looked at the lake water under my microscope at home and saw what I thought was Cylindrospermopsida, but since it is a cylindrical algae and there are more than one type of cylindrical algae, I wasn't positive about what I was seeing. I called Mr. Kevin McCann, who is the Orlando Lake Enhancement Coordinator, and he gave me Julie Bortle's number. She is a researcher at Florida's Environmental Protection Division, and she could help me identify and take pictures of any toxic algae we might find. I went to her lab and we identified Anabaena, Microcystis, and Cylindrospermopsin. We also found Scenedesmus, Agmenellum, and a pennate diatom.
My hypothesis was correct. There are "killer algae" in my lake. But I'm not sure if they warrant the label "killer." They can be very harmful to animals that live in the water and eat large amounts of them, especially when the algae are releasing toxins. They can also be harmful to people who drink algae-contaminated water because the algae release hepatotoxins and neurotoxins (Burns, 2002). This means that the algae can damage your liver and nervous system. The algae exist in Spring Lake because of chemical factors such as storm-water runoff and a lack of shoreline vegetation.
My third question of what to do about the problem is a tricky one. How could I influence people and a golf course to plant native Florida plants on their lakefront property? How could I help make people aware that blowing lawn clippings into storm drains and throwing trash into the street may affect a lake a mile away?
I learned a very interesting thing about Florida's aquifer that may get the public's attention. Florida used to be under the ocean and is actually made up of the remains of the hard shells of sea animals. This created limestone bedrock under the state. Limestone is made up of calcium carbonate, which is dissolved by acidic water. So, under the ground, Florida has a karst topography-which means that it is full of caves that fill up with water. This is where 90% of Florida's drinking water comes from. Only 20 of about 6,400 public water systems use surface water (Drew, 2005). In many other states they do not have underground water to drink-they drink treated surface water. More and more people are moving to Florida and building houses on top of our karst system, which is leading to sinkholes and a loss of aquifer space. The pace of development also means that more people will need water to drink, so at some point we will probably need to start drinking surface water. Currently, there is no way to eradicate toxic algae from the surface water, but filters and treatment plans are being studied (Drew). If we don't take care of the lake water we have, we may need to import drinking water from other states. Maybe an article about Florida's aquifer being in danger would get people's attention as much as the article about "killer algae" got mine.
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